Question

Find the 12^th , 24^th and n^th term of the A.P. given by 9, 13, 17, 21, 25, ………

Answer 1

We have,

a = First term = 9 and, d = Common difference = 4

[∵ 13 – 9 = 4, 17 – 13 = 4, 21 – 7 = 4 etc.]

We know that the nth term of an A.P. with first term a and common difference d is given by a_n = a + (n – 1) d

Therefore,

a₁₂ = a + (12 – 1) d = a + 11d = 9 + 11 × 4 = 53

a₂₄ = a + (24 – 1) d = a + 23 d = 9 + 23 × 4 = 101

and, a_n = a + (n – 1) d = 9 + (n – 1) × 4 = 4n + 5

a₁₂ = 53, a₂₄ = 101 and a_n = 4n + 5